1. Field of the Invention
The present invention relates to a two-stage linked sliding door of a machine tool.
2. Description of the Related Art
A machining space of a machine tool is closed by a cover to prevent chips and coolant from being scattered to the outside. In this arrangement, a sliding door may be provided for loading and unloading workpieces.
For large workpieces, a two-stage sliding door can be advantageously used to provide a larger door opening width. To increase production efficiency, moreover, the door must be quickly opened and closed.
The door opening/closing speed can be smoothly increased by installing a mechanism for associating the operations of two door halves. A mechanism comprising a wire and pulleys is a known as means for interlocking the door halves. An example of this means applied to a machine tool is disclosed in Japanese Patent Application Laid-Open No. 2006-205337.
FIG. 7 is a view illustrating a prior art two-stage linked sliding door of a machine tool. As shown in FIG. 7, plate-like door halves 1 and 2 are attached to an opening (not shown) in a fixed cover of the machine tool, the door half 1 leaving the opening open. In a mechanism using pulleys 3 and 4 and a wire 5, the pulleys 3 and 4 are disposed individually on the opposite ends of a pulley fixing portion 6 that is secured to the door half 2 with a shorter stroke. The wire 5 is secured to the door half 1 with a longer stroke by a wire fixing portion 7.
The wire 5 is secured to a door frame 8 by means of wire tensioning springs 9 and 10. Thus, a wire tensioning spring supporting member 11 is secured to the door frame 8. One ends 9b and 10b of the wire tensioning springs 9 and 10 are anchored to a protrusion, such as a bolt, secured to the wire tensioning spring supporting member 11, while the other ends 9a and 10a are connected to ends 5a and 5b, respectively, of the wire 5. Since the wire ends 5a and 5b are secured to the wire tensioning spring supporting member 11 by means of the wire tensioning springs 9 and 10, the possibility of slacking of the wire 5 due to prolonged use is obviated, and a constant tension can be maintained. In this way, the wire 5 is prevented from being disengaged from the pulleys 3 and 4.
The following is a description of the operations of the door halves 1 and 2. If the door half 1 is moved to the right in the drawing (as indicated by an arrow 101) to close the opening in the fixed cover, the pulley 4, that is, the door half 2, like the door half 1, moves to the right in the drawing (as indicated by an arrow 102). Thereupon, the door halves 1 and 2 move in association with each other. The amount of movement of the door half 2 is half that of the door half 1.
In the above-described arrangement shown in FIG. 7, the wire tensioning springs 9 and 10 lie on the same axis in the direction of movement of the door halves 1 and 2 being opened or closed, so that the length (100) of a wire tensioning portion inevitably increases. In some machine tools, a locking mechanism may be attached to their automatic or non-automatic doors. Since chips and cutting fluid are scattered during machining, mechanical sections, including an automatic door opening and closing mechanism, locking mechanism, linkage mechanism, etc., are often intensively located on the door frame 8 or the like above the door that cannot be easily affected by chips and cutting fluid. Thus, an installation space for the linkage mechanism for the door halves 1 and 2 is limited, so that the mechanical sections are expected to be reduced in size and space.